1.Introduction

Concerns about (1) anthropogenic aerosols affecting possible
global change (Charlson et al., 1992) and (2) acid rain effects on the
environment (Legge and Krupa, 1990) have prompted interest in the
transformation and fate of sulfur in the atmosphere.Aerosols theoretically have the ability to cool the atmosphere
and thus, anthropogenic sulfate particles may be an important factor in the
climate system (Charlson et al., 1992).Their influence might be relatively small regional, or perhaps counter
the entire effect of greenhouse warming in the Northern Hemisphere (Charlson et
al., 1992).The Intergovernmental Panel
on Climate Change (IPCC) report (IPCC, 1994) reconfirmed the ability of
aerosols to affect climate by changing the radiative balance of the atmosphere.

The development of a reliable regional emission
inventory of sulfur as a function of time is an important first step in
assessing the potential impact of sulfate aerosols on climate.A global sulfur emission inventory provides
data for (1) global pollution models; (2) comparisons of sulfur emission patterns
and atmospheric sulfur concentrations; and (3) emission projections.Estimations of sulfur dioxide emissions
since the mid 1800s have been made by Bettelheim and Littler (1979), Dignon and
Hameed (1989), Husar and Husar (1990), Örn et al. (1996), and Mylona (1996),
while others have estimated global sulfur emissions for shorter periods (e.g.,
Kellogg et al., 1972; Cullis and Hirschler, 1980; Möller, 1984; Varhelyi, 1985;
Dignon, 1992; Spiro et al., 1992).Large
discrepancies among the approximations probably reflect the many uncertainties
associated with estimating sulfur emissions.In addition to the above, there are also continental and national
estimates of sulfur emissions (e.g. Gschwandtner et al., 1986; Placet et al.,
1990; Fujita et al., 1991; Kato and Akimoto, 1992).

This paper describes the development of a database that
provides annual estimates of global emissions of sulfur from 1850 to 1990.The period was selected because it included
the onset of 19th century industrialization with rapid growth in
production of fuel and mineral sand the more complex transitions of the 20th
century.A common methodology was
applied across all years and countries; the estimation of emissions was based
on net production (i.e., production plus imports minus exports), sulfur
content, and sulfur retention information associated with that country’s
activities (Husar, 1986).Previous
studies (e.g., Benkovitz et al., 1996) and estimates using alternative
methodologies, (e.g., US emissions estimated by the Environmental Protection
Agency) provided an important comparison with our own results.Our database differs from other global
sulfur emission inventories by (1) detailing the production activities that
lead to sulfur emissions by country and (2) calculating emission for each
year.The application of a common
methodology across all years and countries allows one to improve upon our
estimates, as additional data become available.In addition, our study provides the opportunity to independently
compare our historic global sulfur emission estimates with those of other
investigators.Because the focus of
this study was on annual, national sulfur emission, no attempt was made to
estimate the contribution of sulfur emissions from ships.Corbett and Fischbeck (1997) estimate that
approximately 5% of sulfur emitted by all fuel combustion sources is associated
with sulfur emitted from ships.

2.Approach

The trend in global sulfur emissions was estimated from
production figures (Cullis and Hirschler, 1980; Husar, 1986; Spiro et al.,
1992), relying on national statistics for the extradition of sulfur bearing
fuels and metals.Because there is a
significant international export-import trade in fossil fuels that physically
separates the locations of production and consumption, emission computations
require net production figures.The net
production includes the extraction within the country, plus the imports, and
minus the exports; provided there is no long-term accumulation (bunkering),
consumption will equal net production.Because metallurgical production, rather than mining, gives rise to
sulfur release, emissions were associated with this process.

The emission factors were estimated from sulfur content
derived from (1) fuel and mineral analyses and (2) retention indices.These are spot, not continuous analyses, but
sufficient because individual fuel and ore reservoirs have a reasonably
constant sulfur content.Fuel
combustion and metal smelting liberate some fraction of the solid sulfur into
gaseous sulfur dioxide, the remainder being retained in mineral residues or
ash.Additionally, some may be
recovered or scrubbed from the effluent gases.Sulfur retention or release is estimated from process analysis at the
combustion site (US EPA, 1995a).

Annual sulfur emission rate for a country’s fuel use or
metal extraction can be calculated as a product of (1) net production rate of
fuels and metals, (2) sulfur content, and (3) the release factor.The sulfur emission calculations require
these three parameters for each country, year, and fuel/metal type (i.e., coal,
oil, zinc, lead, copper, and nickel).With the exception of the US, it was assumed that the sulfur content
depended on the country and fuel/metal, but not on time.The switch to low-sulfur coal in the US in
the early 1970s resulted in varying sulfur content of fuels.The sulfur release factor was assumed to
vary with time and extractive process but remain constant worldwide.

Production figures, as well as import/export data were taken
from Mitchell (1981-1983) which covers 1850-1975, although some early figures
are fragmentary.Some of this missing
data was estimated by linearly extrapolating backwards to a time when major use
was assumed to begin: coal and metals, 1850 and oil, 1900.Gaps in the data (e.g., war times) were
bridged by linear interpolation.Metal
extraction figures were not interpolated because the gaps had little impact on
emission estimates.Fortunately little
data were absent for major producers; in all, 234 countries were included in the
database.Production data include
anthracite coal, bituminous hard coal, bituminous brown coal, crude petroleum,
and natural gas, as well as copper, zinc, lead, and nickel.There are some problems of nomenclature of
coals in statistical sources, but our data set labeled anthracite and
bituminous hard coal as hard coal
(with other coals such as lignite and bituminous brown coals labeled as brown coal).

Mitchell’s collection was supplemented by the fuel data set
(Marland and Boden, 1994), prepared by the Carbon Dioxide Information Analysis
Center (CDIAC) from the United Nations Energy database for 1950-1990.Marland and Rotty (1994) estimated that the
uncertainty of the global fuel energy data is about 10%, but the uncertainty
for individual countries is likely to be greater.The CDIAC category coal
production was identified as hard
coal and lignite-brown coal was
identified as brown coal.These assignments produce fairly good
agreement between Mitchell and CDIAC coal figures for overlapping years.Additional mining data came from the
Institute of Geological Sciences (1981, 1982) and the US Bureau of Mines
Statistical Yearbook (1986, 1993), with some gaps filled from UN Statistical
Yearbooks (1952, 1971, 1985) and the League of Nations (1936).Based on the above data sets, the production
database is a homogeneous trend data set of 16 variables, (i.e., import and
export for hard coal, brown coal, crude petroleum, and natural gas, as well as
production data for the metals, copper zinc, lead, and nickel). Lefohn et al. (1996) describe the
consolidation and integration of the various data sets.

The sulfur content of the coals (summarized in Lefohn et
al., 1996) used in this study have been estimated from sources such as the
World Energy Conference (1986Z) and World Energy Council (1992) with additional
information from Husar (1986), Afinogenova and Ryaboshapko (1988), Spiro et al.
(1992), Dianwu (1995), and Kato (1996).The sulfur content of oil is largely based on the Bartlesville Project
Office (1987) that includes virtually all oil producing regions.This compilation provides information on the
sulfur content of gas diesel, jet fuel, motor gas, residual oil, and kerosene
in the US for the period 1955-1990 (summarized in Lefohn et al., 1996).Not all refined products in the CDIAC
database could be assigned sulfur contents from the Bartlesville
compilation.The sulfur content for
refined products in the United States was used for all countries for the time
period defined, except for Asia, where the data from Kato (1996) were
used.We assumed that the refining
technology in practice defined the sulfur content of the refined products.Sulfur from natural gas was set to zero because
its low sulfur content results in relatively small sulfur emissions.A summary of the sulfur content percentages
used in the study can be found on the Internet (http://www.asl-associates.com/sulfur1.htm).

Detailed sulfur content for metals was not available for
individual countries, so US Environmental Protection Agency (EPA) emission
factors for uncontrolled emissions, without sulfur recovery, were adopted (US
EPA, 1995a).The emission factors
expressed as ton of sulfur per ton of the metal produced are: copper smelting
1.2, zinc 0.5, lead 0.14, and nickel 1.20.

The sulfur release factor represents the fraction of the
sulfur in fuels or metal released to the atmosphere, such that complete
volatilization would correspond to a release factor of unity.In general, coal combustion in modern plants
has a release factor close to one, although a small fraction of the sulfur is
retained during coal preparation and in fly ash.If flue gas desulfurization (FGD) is installed, release factors
are substantially reduced.For oil products,
the refining tends to concentrate the sulfur in the heavy residues, such as
residual fuel oil.Metal refining,
where a fraction of the ore sulfur is recovered as a useful byproduct, has a
release factor well below unity.The
sulfur release factors depend largely on the technologies used in the
processing of fuels and metals.The
sulfur release factor for individual countries was not available, so we have
used the same factors for all countries.The aggregated release factors were used to reflect broad historical
trends (e.g., Darmstadter et al., 1987).Charts of aggregate release factors that depict the historical trend of
these factors since 1850 were used.The
uncertainties of these factors are a major contribution to the uncertainty of
sulfur emission estimates.This is
particularly true for sulfur emission estimates associated with the oils and
metals.In our study, the release
factor was decreased from unity in 1850 to 0.47 in 1990.

FGD controls began to be implemented around 1972.Using the cumulative total of thermal
generating capacity information by year supplied by the International Energy
Agency (IEA) in Paris (personal communication) and the cumulative total of FGD
capacity (IEA London, personal communication), it was possible to determine the
percentage of the FGD installed capacity by country by year.Based on information received from the IEA
London (personal communication), the average efficiency of FGD controls by year
was calculated (Table 1).Using
information obtained from OECD (1973-1991), the fraction of coal used in power
plants was obtained by country and year; this information was then combined
with the above data and used in the final emission calculations.

3.Results and discussion

3.1Sulfur production

The worldwide production of anthracite and bituminous hard
coal exceed brown coal production by approximately a factor of three (Fig.
1).Production rose between 1880 and
1910, followed by a plateau until about 1950 and a further rise between 1950
and 1990.World coal production has
doubled since 1950, with brown coal becoming increasingly important.In 1900, the largest coal producing country
was Great Britain, followed by the US and Germany.By 1960, the three major coal-producing countries were China, the
US, and the USSR (Fig. 2), with China dominating by 1990 at 1.1 Gtonne/annum.

The world oil production grew exponentially from 1900 to the
early 1970s (Fig. 1), but fluctuated about 10% over the past 20 years.Import and export figures indicate that
prior to World War II, international oil trade was insignificant, but by the
1960s represented about 50 of the global production.

Since 1850, metal production from sulfur containing
ores (i.e., copper, zinc, lead, and nickel) exhibits a rather varied
behavior.Using the data developed from
this study, Lefohn et al. (1996) found that copper, zinc, and lead have roughly
comparable production rates from 1850 to about 1950.From 1950, copper and zinc production increased by a factor of
3-4, while lead production only doubled.Between 1970 and 1990, the global lead production actually
declined.Nickel production grew from
1930 to 1990, but more slowly than the other three metals.

Fig. 1.Comparison
of global production of anthracite and bituminous hard coal, brown coal, and
oil.

3.2Comparison of global sulfur
emission estimates

Möller (1984) estimated the global anthropogenic sulfur
emissions from 1860 to 2000, and although applying a consistent methodology,
the author used average emission factors rather than country- or
source-specific information.Similarly,
Dignon and Hameed (1989) used statistical models that relate sulfur dioxide
emission to fuel consumption to estimate global emissions at 10-yr intervals
from 1860 to 1980.Using data from
multiple sources, Örn et al. (1996) published global sulfur emission estimates
from 1860 to 1980.At 10-yr increments,
Fig. 3 compares the global emission estimates by Möller (1984), Dignon and
Hameed (1989), and Örn et al. (1996) with this study.Möller’s (1984) figures are consistently higher than the other
studies and may reflect the importance of fuel switching and, in some cases,
the use of FGD controls.The results of
Dignon and Hameed (1989) agree closely with our study.However the authors did not account for
sulfur emissions associated with metal production.Thus, in effect, their reported results represent higher emission
estimates than our own.In comparing
our estimates with those of Örn et al. (1996), we find close agreement.From 1860 through 1930, our estimates are
higher.In the tow decades, 1970 and
1980, the estimated by Örn et al. (1996) were slightly higher.Differences between the sulfur emission
estimates made by other investigators and our study are probably associated
with different assumptions, such as fuel sulfur content and process emissions.

Fig. 2.Comparison
of anthracite and bituminous hard coal production of USSR, China, and the US.

Fig. 3.Comparison
of global sulfur emission estimates.

Spiro et al. (1992) determined sulfur emissions for all
countries.Applying their methodology
for all countries, the authors reported 88.4 Mtonne of anthropogenic sulfur emissions
for 1980.The authors substituted their
estimates for Europe, the USSR, North America, and Japan with existing
inventories developed b the individual countries and recalculated global
anthropogenic sulfur emissions at approximately 78 Mtonne.Our estimate for 1980 was approximately 66
Mtonne.The estimates by Spiro et al.
(1992) were used by Örn et al. (1996).The values reported for 1985 and 1990 by Benkovitz et al. (1996), using
an entirely different protocol than the one used in our study, were almost
identical to ours (i.e., approximately 65 and 71.5 Mtonne, respectively).

In 1985, the European Council of Ministers made a decision
to form a Commission for gathering, coordinating, and ensuring the consistency
of information on the state of the environment and natural resources in the
European Community.One of the
components of the program was the CORINe AIR emission inventory
(CORINAIR).Estimates of sulfur emission
in Europe were made for 1985 and 1990 by CORINAIR (US EPA, 1995b), and Mylona
(1996).For example, in 1990, except
for a few countries (e.g., Germany, Bulgaria, and Italy), the European
estimates from this study were close to CORINAIR (Fig. 4).Differences between the sulfur emission
estimates may be associated with differences in the published production levels
that we used and modified government statistics.

One geographic area where our estimates disagreed
considerably was Japan.Sulfur emission
estimates made by Kato (1996) for Japan ranged from 37 to 66% of estimates made
in this study.Our study considered
FGD, but not coal washing, which may account for part of the lower values
published by Kato (1996).We do not
have a full explanation for the difference between our results and those of
Kato (1996).

The EPA (1995b) summarized trends for the US for the period
1900-1994, identifying a downward trend from the mid-70s.However, our study suggests level emissions
from the mid-70s to early 80s, a downward trend until the mid-80s, and then a
gradual increase into the 90s.We estimated
US emissions at 10.8 and 12.5 Mtonne for 1985 and 1990, while the EPA estimated
10.6 and 10.2 Mtonne.Applying the data
from our study, Lefohn et al. (1996) suggest some of the difference that occurs
after 1985 between our estimates and those of EPAs may be associated with the
consumption of residual fuel oil.In
addition, the EPA (1994) assumed sulfur dioxide and PM10 controls to
be totally effective, while our study rated sulfur controls only 85% efficient.

Fig. 4.Comparison
of estimates of European sulfur emissions.

3.3Estimated global sulfur
emissions

Since 1850, the global anthropogenic sulfur emission trend
for 1850-1990 shows that there has been a general increase of sulfur emissions
(Fig. 5).We estimate that emissions in
1850 (approximately 1.2 Mtonne) were about 1.7% of the current values (71.5
Mtonne).There was some leveling off,
beginning in 1913, with a decline during World War I.The great depression (1930-1932) led to a marked decrease in
global emissions with increases in 1933 through 1944, partly associated with
World War II.The postwar years saw a
continuous increase, with a drop in 1981-1983, resulting primarily from
declining oil demand during the global recession.Fig. 5 compares emissions from North America, Europe, and
Asia.While North American, and in some
cases, European emissions have been leveling off, rapid increases are occurring
in Asia.

Fig. 5.Estimated
sulfur emissions for Europe, North America, and Asia.

The effect of sulfur emissions in the US as a function of
applying different corrections is shown in Fig. 6.The corrections sued in our study were (1) FGD controls, (2) the
switch to low-sulfur coal (2.3-1.3%, from 1973 to 1990), and (3) increased
retention in oil refining on US emissions.The top line shows the level of sulfur emissions that would have
occurred if corrections were not applied.The bottom line reflects estimated emissions using the corrections
implemented in our study.Note that the
bottom line and the line representing no FGD controls are close to one
another.Alternatively, the line
representing the effects of applying no FGD controls and fuel switching is much
higher than the line representing no FGD controls.This observation implies that FGD controls had much less impact
on sulfur emissions than switching to low-sulfur coal.Reviewing the data from our study, we found
that globally, flue gas desulfurization (FGD) has made important contributions
to emission reductions in only a few countries, such as Germany (Lefohn et al.,
1996).

Fig. 6.The effects
on sulfur emissions as a function of applying different corrections using data
from the United States (w/o is substituted for the word “without”).

Fig. 7 shows that the US, the USSR, and China were the main
sulfur emitters in the world in 1990.The USSR and US appear to have stabilized their emissions over the past
20 years, such that recent increases can be linked to industrialization in
China.In 1990, these three countries
accounted for 53% of the global sulfur emissions.

Using our data, Lefohn et al. (1996) discuss the changes in
sulfur emissions over the years.The
authors note that the combustion of coal is the dominant anthropogenic source
of sulfur.The contribution from oil
products rose rapidly between 1950 and 1980, but has fluctuated from 1980 to
the present.Sulfur emissions
associated with copper smelting peaked in 1974.Therefore, the steady increase in emissions since the 1970s is
attributable to increased coal combustion.The US shows substantial sulfur emissions from hard coal prior to 1940;
China and the USSR emitted insignificant quantities in the first half of the 20th
Century.Sulfur emissions from brown
coal are mainly from Europe.

Major emissions from oil consumption occur in the US, the
USSR, and Saudi Arabia, with significant contributions from Mexico, China, and
Japan.Historically we see an early
dominance by the US and the subsequent emergence of the other two major
emitters since the 1950s (Lefohn et al., 1996)

The sulfur emissions from copper show an identical pattern
to copper production, because both sulfur content of ores and the release
factor were assumed to be geographically constant.Since 1910, the copper-related emissions from the US have fluctuated,
while there have been steady increases from Chile since 1920 (see Lefohn, et
al., 1996).In 1990, the primary
emitter was Chile, where the emissions of 0.9 Mtonne were a major part of its
contribution.The USSR and Canada
dominate emissions associated with nickel production, while major zinc-related
emissions arise from Canada and Australia.Lead-derived emissions are relatively small (i.e., less than 0.04
Mtonne), with the largest in 1990 from Australia, the US, and the USSR.In many smaller countries, where mining
makes a big contribution to the economy, metallurgical emissions can be the
dominant source of anthropogenic sulfur.

Fig. 7.Change in
major sulfur emitters in comparison to remainder of the world.

4.Conclusion

This study estimated annual national sulfur emissions from
1850 to 1990, based on net production, sulfur content, and sulfur release
factors for each country’s production activities, using a common methodology
applied across all years and countries.In 1990, the spatial pattern of emission shows that the US, the USSR,
and China were the main sulfur emitters (i.e., approximately 50% of the
total).While the USSR and the US
appear to have stabilized their sulfur emissions over the past 20 years, recent
increases in global emissions are linked to the rapid industrialization in
China.Combustion of coal remains the
dominant anthropogenic source of sulfur.The US and Europe, unlike China and the USSR, showed substantial sulfur
emissions from hard coal prior to 1940.Although the contribution from oil products rose rapidly from 1950,
growth has fluctuated since 1980.Major
emissions from oil consumption occur in the US, the USSR, and Saudi Arabia,
with significant contributions from Mexico, China, and Japan.Historically, we see an early 20th
Century dominance by the US and the subsequent emergence of the other two major
emitters since the 1950s.Sulfur
emissions have been reduced in some cases by switching from high- to low-sulfur
coals.Flue gas desulfurization (FGD)
has made important contributions to emission reductions in only a few
countries, such as Germany.

Acknowledgements

The authors wish to acknowledge Professor Peter
Brimblecombe, University of East Anglia, Norwich, UK, for his assistance in
locating data that were used in developing the emission estimates.One of the authors (ASL) wishes to
acknowledge the US Department of Energy support under Research Grant
DE-FG0694ER30234.In particular, we
thank Dr. Walter L. Warnick of the Office of Program Analysis, Office of Energy
Research, Department of Energy, for his technical guidance.In addition, the authors acknowledge the
following individuals and organization for providing key references and data
during this research project: Ms. Dottie Karsteter, National Energy Information
Center, the United States Energy Information Administration, Washington, DC;
Ms. Bernadette Michalski, Office of Minerals Information, Geologic Survey,
Department of the Interior, Reston, VA; Ms. Irene Smith, Environmental Group,
International Energy Agency Coal Group, London, England; Dr. Eric Savage,
Energy Statistics Division, Combined Energy Staff, International Energy Agency,
Paris, France; Ms. Cheryl Dickson and John Green, BDM, National Institute for
Petroleum and Energy Research, Bartlesville, OK; Mr. Igor Soyfer of CAPITA for
data compilation; Dr. Gregg Marland, Environmental Sciences Division, Oak Ridge
National Laboratory, Oak Ridge, TN.

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